Electromagnetic chuck



S. KARASICK ELECTROMAGNETIC CHUCK Filed May 4, 1935 INVENTOR SAMUEL KARASICK ATTORNEY ml Q Q Patented July 6, 1937 UNITED} STATES PATENT OFFICE Application May 4,

9 Claims.

This invention relates to improvements in electromagnetic chucks and more particularly to the top or work supporting plates for such chucks.

Attempts have been made to utilize non-magnetic and non-conducting material, for example a molded phenol condensation product commonly called bakelite, as a binder for the parts of a top or work holding plate of an electromagnetic chuck, such as is disclosed in my prior Patent #l,301,l35. It has been found that a top plate constructed with a rigid frame in which the laminated pole pieces are embedded in such a molded condensation product, is not practical especially for wet grinding operations. This is due to the fact that if the condensation product is forced under moderate pressure into the spaces between the pole pieces and the frame of the top plate, the resulting shrinkage of the product develops leaks at the junction thereof with the edges of so the pole pieces and the frame, particularly at the inner edge of the frame. If however, sufiicient pressure is applied to the condensation product to overcome the mentioned shrinkage, this pressure usually results in the cracking of the frame which cannot withstand the stresses set up therein, unless it is made of such size and thickness as to be unacceptable commercially.

It has been proposed to utilize an all molded bakelite top plate without a metal supporting frame, but such a construction does not have sufficient mechanical strength to withstand the severe usage to which it is subjected, and furthermore, the necessary T-slot at the front of the frame cannot be made in bakelite without weakening it to the point where it is practically useless.

If, on the other hand, a built up structure is utilized instead of a molded one, the design involves complicated parts and results in greatly increased costs, while the bolts or other members relied upon to secure these parts tightly together, tend to become loosened by vibration especially when the chuck is energized by alternating current.

In accordance with the main feature of the present invention, it is proposed to make a workor top plate of an electro-magnetic chuck of bakelite or other phenol condensation product, suitably reinforced by metal strengthening members which are free to expand and contract with the bakelite so that the top plate does not develop cracks and leaks therein.

A further feature of this invention relates to the provision of a top plate for a magnetic chuck, which is composed mainly of non-conducting, non-magnetic material, except for the pole pieces carrying the magnetic flux, but is provided with reinforcing members of a non-magnetic but conducting metal, the said reinforcing members being so disposed that no closed, electrically con- 1935, Serial No. 19,868

ducting loops are thereby formed about any or all of the pole pieces, since it has been found that the elimination of such conducting loops is essential for the successful operation of a combined chuck and demagnetizer.

Other features of the invention will appear from the detailed description and claims when taken with the drawing, in which Fig. 1 is a plan view of the top or work supporting plate of an electro-magnetic chuck; Fig. 2 is an end view of 'the plate of Fig. 1; Fig. 3 is a fragmentary sectional view of an electro-magnetic chuck provided with the improved top plate of the present invention on line 3-3 of Fig. 1 and Fig. 4 is a cross sectional view thereof.

Referring to Fig. 3, 5 designates a combined aluminum casing and base of an electromagnetic chuck. This casing has mounted therein a core element 6 built up from a plurality of laminae riveted together, each of which laminae is stamped from a ferro-magnetic material such as Norway iron, and is provided with a plurality of integral uprights or core elements 1. Each of the uprights or core elements has mounted thereon a spool 8 including a coil or helical winding, of the type well known in the art, adapted to develop a magnetic flux in said core elements when electric current flows through the mentioned winding or windings. A suitable circuit arrangement for energizing the several windings of the chuck is disclosed in applicants co-pending application, Serial No. 691,048.

A top plate Ill is provided with a'series of pole pieces ll made of magnetic laminae riveted together, which pole pieces areof such dimensions and are so spaced in the plate, that one of them is in physical contact with the upper end of each core element 1 of the core when the plate is attached to the casing of the chuck. Molded phenol condensation material 12 such as bake lite, encloses the series of pole pieces and fills the spaces therebetween. In order to give the top plate sufficient strength so that it is commercially useful, the molded-material is suitably reinforced by reinforcing members. These members include, at the front of the top plate, a metal bar i3 having formed therein 'a T-shaped work slot H in the top thereof, while at one edge of the bar there is provided a longitudinally extending dove tail 15. This dove tail interlocks with the bakelite which is forced into engagement with the bar. The bar I3 is provided in its underside with tapped openings 16 by which one margin of the plate can be attached to the chuck casing by bolts 25 (Fig. 4) Each end of the top plate is reinforced by a metal rod 11 having one of its ends screwed into a tapped opening in the dove tail I5 near one end of the bar while the other end of each rod projects to a point near the opposite edge of the finished plate. Each rod 11 passes through an opening in each one of a pair of rectangular inserts i8 embedded in 'the bakelite. It should be understood that the rod I1 is not fastened to the inserts l8 but is freely movable therethrough to permit expansion and contraction of this rod. Each insert i8 has a tapped opening l9 therein useful during the molding of the top plate. 'The rear margin of the top plate is reinforced by a rod 20 extending to points spaced slightly from the ends of the rods I! so that there will be no contact therebetween. The rod 20 freely passes through an openingin each of the rectangular inserts 2| embedded in the bakelite". These inserts have tapped openings 22 therein also useful during the molding of the top plate. The rod 20, likewise, freely passes through an opening in each of the cylindrical inserts 23 which have tapped openings 24 therein accessible from the bottom of the plate to permit the rear margin of the plate to be fastened to the casing by the bolts 26. y

In the making of the top plate, the pole pieces H are placed in' spaced'relation as illustrated on a flat surface within a frame (not shown). The bar I3 having the reinforcing rods I1 screwed therein and with these rods passing through the openings in the metal inserts l8 are likewise placed on the flat surface within the frame,

the outside edgeof the bar engaging an inner edge of the frame. The frame may -have bolts or other supports to engage thetapped openings IS in these inserts to hold them in the position illustrated. The rod 20, with theinserts 2| and 23 mounted thereon, is placed within the frame and'the rod 20 is held in its proper position by means of bolts or other supports (not shown) in the frame engaging the tapped openings in the inserts 2|. With the parts thus positioned, bakelite isforced into the resulting spaces around these parts within the frame. When the bakelite" has solidified the bolts in the frame are removed from the inserts i8 and 2| and the plate is removed from the frame. The plate is then fastened to the casing 5 by'means of the bolts 25 and 26.

A top plate constructed in this manner, is easily manufactured, is amply strong to resist the hard usage to which it is normally subjected, and does not develop cracks due to the unequal expansion and contraction of its parts.

What I claim is:

1. In an electromagnetic chuck having core elements and energizing coils therefor, a top plate of molded non-magnetic, non-conducting material, said top plate having pole pieces embedded therein to coact with said core elements, and bar-like reinforcing members embedded in said top plate in a position to define a discontinuous frame-enclosing said pole pieces.

2. In an electromagnetic chuck' including a casing having core elements and energizing coils therefor mounted therein, a top of molded, nonconducting, non-magnetic material having pole pieces embeddedtherein to coact with said core elements, metal reinforcing members embedded in said top in a. position to define a discontinu ous frame enclosing said pole pieces, said members being of a length approximately equal to the length and breadth of said top and means engaging certain of said members to fasten said top to said casing.

3. In a top plate for an electromagnetic chuck. said top plate being molded of non-conducting,

non-magnetic material and comprising a plusaid material adjacent the edge of said plate opposite said bar and extending generally parallel to said bar.

5. In a top plate for an electromagnetic chuck, said top plate being molded of non-conducting, non-magnetic material and comprising a plurality of pole pieces embedded in said material,

a bar at one edge of said plate having rods projecting therefrom into said material, inserts embedded in said material through which said rods freely pass, another rod embedded in said material adjacent the edge of said plate opposite said bar and extending generally parallel to said bar, and other inserts embedded in said material through which said other bar freely passes.

6. In an electromagnetic chuck, including a casing of non-magnetic material having core elements and energizing coils therefor mounted therein, a molded non-conducting, non-magnetic top having laminated pole pieces embedded therein to coact with said core elements, reinforcing metallic members embedded in said top, certain members being arranged as a frame around said pole pieces, certain of said members being out of engagement with each other whereby the formation of any electrically conducting paths around the said pole pieces is avoided.

7. In a top plate for an electromagnetic chuck, said top plate being molded of non-conducting, non-magnetic material and comprising a plurality of pole pieces embedded in said material, and a bar at one edge of said plate having rods projecting therefrom into said material.

8. In a top plate for an electromagnetic chuck, said top plate being molded of non-conducting, non-magnetic material and comprising a plurality of pole pieces embedded in said material, a bar at one edge of said plate having rods projecting therefrom into said material, and another rod embedded in said material adjacent the edge of said plate opposite said bar and extending generally parallel to said bar.

9. In a top plate for an electromagnetic chuck, said top plate being molded of non-conducting, non-magnetic. material and comprising a plurality of pole pieces embedded in said material, a bar at one edge of said plate having rods projecting therefrom into said material, another rod embedded in said material adjacent the edge of said plate opposite said bar and extending generally parallel to said bar, and other inserts embedded in said material through'which said other bar freely passes.

SAMUEL KARASICK. 

